Field of the Invention
The invention relates to a method and an apparatus for measuring flow velocities of all components of a fluid flowing in a delivery line that interact with electromagnetic waves.
The measurements of the flow velocities and volumetric flows of fluids which have one or more components and/or phases, form the basis of every industrial process management. In the methods used to date for such measurements, the determination of the volumetric fractions and the determination of the flow velocities of the components of a fluid are performed separately from one another. The measuring apparatus is thus also split up into two or more devices. In this case, one device is used to determine the volumetric fractions, while a second device is used to determine the velocities. The determinations of the velocities and volumetric fractions are, moreover, not performed at the same point in the known methods. Due to this spatial separation, the measurements of the velocities and the volumetric fractions are effectively carried out at different times. Furthermore, it must be taken into account that the flow profile changes with time in many instances. If the velocities and volumetric fractions are determined from the correlation of such measurement signals of spatially separated measuring devices, the time dependence of the flow leads to a substantially reduced resolving power, with the result that measurement results that are more inaccurate are determined overall.
British Patent No. GB 2 271 637 B, corresponding to U.S. Pat. No. 5,389,883, describes a method with the aid of which it is possible to determine the volumetric fraction of gas and water in crude oil which is flowing through a delivery line. The respective volumetric fractions are determined with the aid of electromagnetic signals of high frequency, and the resonance signals thereof.
U.S. Pat. No. 5,792,962 discloses a method in which in order to measure the velocities of components of a fluid, use is made of the influence of the latter on the propagation characteristic of electric or acoustic signals which are led through the fluid.
U.S. Pat. No. 5,793,216 discloses a device for determining flow rates by conducting electromagnetic waves through a fluid. The fluid interacts with the electromagnetic waves and thus with the signal conducted through the fluid. The Doppler shift between the original electromagnetic signal and the resulting electromagnetic signal determines the velocity of the fluid.
Also known are measuring apparatuses in which high energy radiation in the form of X-rays or y-rays is used to determine the velocities and volumetric fractions of the components of a fluid. Because of this radiation, these devices are in part structurally very complex. Moreover, they must be provided with additional safety precautions.
The resolving power is mostly unsatisfactory in the known methods, in which the velocities and volumetric fractions of the components of a fluid are determined with the aid of the Doppler effect and electromagnetic radiation which has a low frequency of between 0 GHz and 1000 GHz. Because of the exceptionally low ratio of the average flow velocity of 5 m/s or less of a fluid to the speed of light in vacuum, frequency shifts which often cannot be resolved result for radiations in the GHz region specified above. Thus, the Doppler frequency shift resulting from the equation df=2(v/c)f is at only approximately 30 Hz for f=1 GHz and v=5 m/s.
It is accordingly an object of the invention to provide a method and an apparatus for measuring flow velocities which overcome the above-mentioned disadvantages of the heretofore-known methods and devices of this general type and with the aid of which the flow velocities and the volumetric fractions of all components of a flowing fluid which interact with electromagnetic waves can be determined in a simple way.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for determining flow velocities, the method includes the steps of:
conducting at least one electromagnetic signal having a frequency of between 0 GHz and 1000 GHz through a fluid flowing in a delivery line, the fluid having components interacting with electromagnetic waves, and additionally conducting the at least one electromagnetic signal in a spatially delayed manner; and
determining a velocity, a velocity profile and a volumetric fraction of each of the components of the fluid from a Doppler shift between an original electromagnetic signal and a resulting electromagnetic signal.
In other words, a method for determining the flow velocities of all the components of a fluid flowing in a delivery line which interact with the electromagnetic waves is provided, wherein at least one electromagnetic signal with a frequency of between 0 GHz and 1000 GHz is conducted through the fluid and, additionally, spatially delayed, and in that the velocity, the velocity profile and the volumetric fraction of each component is determined from the Doppler shift between the original and the resulting signal.
The method according to the invention is used to determine the flow velocities and the volumetric fractions of the individual components of a fluid from the interaction of low-frequency electromagnetic radiation with the fluid. Use is made in this case of the cost-effective availability of electronics which are capable of utilizing the low-frequency electromagnetic measuring signals. An electromagnetic signal with a frequency of between 0 GHz and 1000 GHz is firstly generated with the aid of a signal generator. This signal is led through a delay line and through the fluid to be investigated. The delay line is arranged inside a metallic screen. The latter also surrounds the delivery line through which the fluid is transported. The velocity, the velocity profile and the volumetric fraction of the components of the fluid can be determined from the Doppler shift between the original and the resulting signal. Provided for this purpose is an evaluation unit which is fed two signals.
With the objects of the invention in view there is also provided, in combination with a delivery line having a fluid flowing therethrough, the fluid having components interacting with electromagnetic waves, an apparatus for determining flow velocities of the components of the fluid, including:
a screen partially surrounding the delivery line;
a delay line disposed within the screen;
a signal generator providing a low-frequency output signal to be coupled into the delay line;
a connecting element; and
at least one coupling element projecting, via the connecting element, into the screen.
In accordance with another feature of the invention, the at least one coupling element is connected to the signal generator.
In accordance with another feature of the invention, an evaluation unit is connected to the at least one coupling element.
In accordance with yet another feature of the invention, the screen is a metal screen having a given length and completely surrounds the delay line; and the signal generator is configured to generate electromagnetic signals with frequencies of between 0 GHz and 1000 GHz.
In accordance with a further feature of the invention, the delay line is a helical line wound around the delivery line.
In accordance with another feature of the invention, the at least one coupling element is an antenna.
With the objects of the invention in view there is also provided, an apparatus for determining flow velocities, including:
a delivery line configured to transport a fluid having components interacting with electromagnetic waves;
a screen partially surrounding the delivery line;
a delay line disposed within the screen;
a connecting element;
at least one coupling element projecting, via the connecting element, into the screen;
a signal generator providing a low-frequency output signal to be coupled into the delay line; and
an evaluation unit operatively connected to the at least one coupling element and determining flow velocities of the components of the fluid.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a measurement method and an apparatus for carrying it out, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.